This invention relates to a novel method of assembling the mount assembly in the neck of a cathode-ray tube.
Most cathode-ray tubes are used for displaying video images; for example, in displays for television, radar and computer systems. A tube used for such applications includes a bulb or envelope comprising a faceplate panel having a viewing window which supports a luminescent screen on its inside surface, a neck which houses and supports a mount assembly, and a funnel which connects the neck with the panel. During fabrication, the screen, window and funnel are assembled, and then the mount assembly, which includes a disc-shaped glass stem, is sealed into the neck. This latter step is referred to as mount sealing.
The mount assembly includes at least one electron gun which generates and projects at least one electron beam toward the screen for exciting the screen to luninescence when the tube is operating. The mount assembly may include also snubbers or bulb spacers, which are springlike fingers, at the opposite end of the mount from the stem for spacing the mount assembly from the neck. The mount assembly may also include an antenna getter which comprises a getter container attached to one end of a long, flat spring, which in turn is attached at its other end to the mount assembly. The spring urges the container against the inside of the funnel.
The funnel is coated on most of its inside surface with an electrically-conducting coating, usually including graphite and a binder therefor. The inside funnel coating extends under the getter container and under the bulb spacers down to the electron gun or guns. The inside neck surface opposite the guns is usually bare glass, but sometimes part or all of the surface has an electrically-resistive coating thereon.
During mount sealing, the panel-funnel assembly; that is, the assembled panel, screen, funnel, inside funnel coating and neck, is positioned in a holder. The antenna getter and bulb spacers are depressed and inserted by hand inside and near the open end of the neck. Then, the stem leads and stem are seated on a mount pin, and the mount assembly is rotationally oriented with respect to the screen. Now, the mount assembly is slid in the neck toward the screen to the desired spacing from the screen while maintaining its rotational orientation. Mount sealing is described previously; for example, in U.S. Pat. Nos. 3,807,006 to J. F. Segro et al and 2,886,336 to C. G. Reynard.
During the steps of inserting and sliding the mount assembly toward the screen, the getter container and the bulb spacers slide first on the bare glass surface of the neck and then on the inside funnel coating. It is believed that particles are liberated during this step, and in some cases the parts bind on the glass surface and/or funnel coating and scratch the surface beneath. Any particles which are generated are undesirable in the tube, since they may cause a variety of problems in the operation of the completed tube. Conducting particles, particularly in the neck region, may provide sites from which high-voltage arcing may occur. Insulating particles, wherever they exist in the tube, provide sites on which electrostatic charge can accumulate, producing localized electrostatic fields which may interfere with the cathode-ray beam or beams. Also, scratches on the bare glass may result in breakage of the glass during subsequent thermal cycling.